Arrange in order of decreasing trend towards ${\mathrm{S}}_{\mathrm{E}}$ reactions:

(I) Chlorobenzene

(II) Benzene

(Ill) Anilinium chloride

(IV) Toluene

The order of decreasing trend towards ${\mathrm{S}}_{\mathrm{E}}$ reaction is Toluene > Benzene > Chlorobenzene > Anilinium chloride.

Due to the -I effect, chlorobenzene is less reactive than benzene in electrophilic substitution reactions. Since chlorine is an electron-withdrawing group, it deactivates the benzene ring, lowers its electron density, and lessens its reactivity toward incoming electrophiles.